In a prior art, significant developments have been made for non-destructively testing surface and near surface conditions on samples. For example, the assignee of the subject invention has developed a number of special techniques for measuring surface and subsurface conditions in the sample. In U.S. Pat. No. 4,521,118, issued on June 4, 1985, and U.S. Pat. No. 4,522,510, issued on June 11, 1985, a technique is disclosed for detecting thermal waves using a laser beam deflection system. The detected thermal waves are used to evaluate thermal parameters in the sample.
In U.S. Pat. No. 4,579,463, issued on April 1, 1986, a second technique is disclosed for detecting thermal waves. This technique relies on the measurement of periodic changes in optical reflectivity of the sample as it is periodically heated by a modulated pump source. The apparatus for performing this technique can also be used to evaluate semiconductor samples as disclosed in U.S. Pat. No. 4,636,088. In a semiconductor, the modulated pump source functions to generate plasma waves in the sample which have a direct effect on its optical reflectivity. This technique can provide very useful information on ion-dopant concentrations and about the etching steps. The generation and detection of plasma waves is described in U.S. patent application Ser. No. 707,485, filed on Mar. 1, 1985, assigned to the same assignee as the subject invention. The physics underlying the device disclosed in the latter patent application is described in "Thermal and Plasma Wave Depth Profiling in Silicon" Applied Physics Letters, Opsal and Rosencwaig, Volume 47(5), page 498, Sept. 1, 1985. All of the above patents and the latter application and article are hereby incorporated herein by reference.
As will be discussed below, the apparatus of the subject invention utilizes a beam of radiation to search out and locate areas of interest on a workpiece. Each of the above described techniques for evaluating samples also employs at least one beam of radiation. For this reason, the measurement devices developed by the assignee herein are particularly suited to form a portion of the subject invention since much of the existing hardware in the prior art devices can be modified to sense and locate areas of interest on a workpiece.
One of the biggest difficulties facing the semiconductor industry is poor fabrication yields. The principal reason for such low yields is the lack of a totally clean environment. Contamination can most often be traced to handling of the wafers by human personnel. Therefore, significant effort has been expended in trying to develop machinery which will automate the manufacturing process.
Much of the automated equipment in use today consists of handling devices used to move semiconductors from one area to another. There also exist relatively sophisticated inspection systems which include complex machine imaging systems. The imaging systems are used to locate and inspect specific regions on the semiconductor wafer. As is well-known, semiconductors are manufactured by a plurality of masking steps. Areas within the mask are etched and then treated through subsequent process steps. Some inspection equipment has been designed to determine if the proper etch pattern has been laid down on the semiconductor. In order to achieve this result, a highly sophisticated pattern recognition system must be used. One such pattern recognition system is disclosed in U.S. Pat. No. 4,597,669, issued July 1, 1986 to Terasawa. These pattern recognition devices require high speed microprocessors and large memory storage capacity.
While such a sophisticated system provides information about the entire pattern on the wafer, such information is often unnecessary. For example, many inspection or test procedures developed by the industry require only minimal point testing in unmasked areas. The exact location of the points to be tested is not particularly critical as long as the points are located in unmasked areas that are spaced out over the entire wafer. If the measured results of these tested points fall within the specified fabrication parameters, there is a reasonable probability that the manufacturing process has been properly carried out. In the latter approach, the test device would only need to be able to reliably locate unmasked areas on a semiconductor wafer, and the complex processing and storage requirements of a pattern recognition systems would be unnecessary.
Accordingly, it is an object of the subject invention to provide a new and improved method and apparatus for testing areas of interest on a workpiece where the areas of interest have an optical reflectivity different from the other areas on the workpiece.
It is a another object of the subject invention to provide an new and improved method and apparatus for identifying areas of interest on a workpiece for subsequent testing.
It is a further object of the subject invention to provide a new and improved method for identifying the unmasked areas on a semiconductor wafer.
It is another object of the subject invention to provide a new and improved method for identifying unmasked areas on a semiconductor wafer for subsequent testing.
It is a further object of the subject invention to provide a new and improved method for identifying unmasked areas on a semiconductor wafer which can then be tested for ion dopant concentrations.
It is still a further object of the subject invention to provide a new and improved apparatus for identify unmasked areas on a semiconductor wafer which can then be tested for the effects of processing steps such as etching procedures.
It is still another object of the subject invention to provide a new and improved apparatus which relies on the optical reflectivity of the surface of the sample to locate unmasked areas on a semiconductor wafer.
It is still a further object of the subject invention to provide a new and improved apparatus for identifying areas of interest on a workpiece utilizing a reflected search beam.
It is still another object of the subject invention to provide a new and improved apparatus wherein the search beam used for identifying the location of an area of interest on a workpiece, such as a semiconductor wafer, is subsequently used in the testing procedure.